Froth flotatation of sulfide ores



Patented May 24, 1949 2,471,384 FROTH FLOTATION OF SULFIDE QRES Robert B. Booth, Springdale, and Roy A. Pickens,

Stamford, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application May 16, 1946,

7 Serial No. 670,313

3 Claims.

This invention relates to the beneficiation of metallic sulfide aration of one or more metal sulfide minerals each from the other and/or from other minerals or gangue, particularly slimy gangues. As such the present invention constitutes a continuationin-part of our copending application, Serial No. 639,164, filed January 4, 1946.

The term sulfide ores as used herein is employed in the broad sense to describe those ores whose mineral values are mainly in the form of sulfide minerals and also to describe ores whose values may be in the form of sulfide minerals associated with other values in the form of native metal and oxide or oxidized minerals. Forexample, copper ores frequently contain a portion of their values as sulfides, chalcocite, covel-. lite, and chalcopyrite associated with pyrite, molybdenite, native copper, cupri-te,bornite, azurite, malachite and chrysocolla. Similarly lead sulfide ores frequently contain galena associated with cerrusite and anglesite, while zinc ores often ores and in particular to the sepcontent of copper mineral in the concentrate. Beyond a certain point, however, increasing the copper content of the concentrate is done at the expense of increasing the copper content of the tailing. A practical economic balance therefore must be made and subsequently followed as nearly as possible in which the degree of concentration and the copper content in the tailing are both considered in determining .the optimum recovery.

Unfortunately, even good practice with the better promoters frequently will not permit reducing the copper content of the tailing to a point as low as is desired without producing a less than premium grade concentrate. This problem has faced the art for many years and many auxiliary agents have been suggested for modifying the action of the promoter during flotation, without fully accomplishing the desired results. It is therefore the principal object of the present invention to develop a surface-modifying agent for use in the beneficiation of sulfide ores which contain sphalerite associated with willemite,

smithsonite and calamine.

Beneficiation of metallic sulfide ores by froth flotation has come to be commonly accepted as almost a standardized procedure. The process is carried out in acid, neutral or alkaline circuits in the presence of a promoter and, usually, a frothing agent. Many materials have been suggested for use as promoters. The most widely accepted in use have come to be the xanthate and dithiophosphoric acids and dithiophosphate types. These have been found excellent and have achieved almost universal acceptance.

However, it must be realized that in such operations a relatively tremendous amount of feed is handled to obtain a relatively small amount of desirable mineral in the concentrate. Consequently the amount of valuable material left in the tailing is a highly important factor. Usually the more the mineral value content of the tailing can be reduced the more highly satisfactory the operation. In addition thereto, there is the problem of obtaining a high ratio of concentration. Usually this latter is of primary importance, the grade of concentrate being the most critical measure of the degree of success of the operation. At times, however, the freedom of the tailing from valuable mineral content may become equally if not more important.

The difiiculty may be illustrated, for example,

in the concentration of copper minerals from a typical feed containing other sulfides such as those of lead or zinc or both, gangue and secondary slimes. Using a good commercially available romoter, it is frequently possible to produce copper sulfide concentrates which may be of higher grade than the commercially acceptable minimum. It is ordinarily desirable to do so since premiums are usually paid based on the higher when properly used will enhance both the selectivity and the collecting power of the better of the presently available promoters. At the same time it is desirable that the modifying agent or agents be readily available, relatively inexpensive, easily used and capable, once their optimum use is determined, of reliably duplicating the desired result.

Surprisingly these desirable results are simply and easily obtained by using the proper amount of a suitable lignin sulfonate as the surface modifier for the mineral constituents of the flotation pulp. Although this type of reagent appears to have the effect of such a surface-modifying action on the minerals, the exact nature of its action is not wholly understood. Their action, however, is highly reliable. As shown in our above identified copending application, in the beneficiation of copper sulfide minerals, for example, they may be used to reduce the copper content of the tailing by as much as one-half.

In addition to this valuable property, in accordance with the present invention it has also been found that their surface-modifying effect is progressively selective. Thus, by the proper use it is perfectly feasible to progressively separate with a high degree of concentration first one sulfide mineral and then another. practices are familiar in the art of treatment of mixed ores containing a plurality of valuable minerals. In the separation of one sulfide mineral from another the lignin sulfonates used in accordance with the present invention are selectively effective in each of the separation, appearing to enhance the collection of the desired fraction by the promoter while depressing the other sulfides and/or other undesirable mineral values and gangue.

These The form in which the lignin sulfonate is used in the practice ofthe present invention i's'not necessarily critical in most cases. If desired it may be used inacid form. The amount used is not sufficient to markedly alter the pH of a neutral circuit. Therefore whether an acid form is fed to an acid or alkaline circuit makes little difference. Nor does it appreciably alter the process if an alkaline lignin sulfon-ate is added to either an acidic or alkaline circuit.

In general the alkali metal or alkaline earth metal lignin sulfonates including the ammonium salts are preferable because they are available commercially either in the form of solutions or as dry powders. The latter are easily shipped to the point of use, are readily soluble in water and may be fed without difficulty. The sodium, ammonium, calcium, barium and magnesium salts as well as mixtures thereof have been successfully used. Lignin sulfonates for use in the present invention may be either purposely synthesized, or commercially available products may be used. These latter, derived usually from the manufacture of pulp and paper, are often obtainable in highly purified condition. However, for the purpose of the present invention this is not essential. In many cases the degree of purity appears to be of concern only in so far as it effects the amount to be used. Since the crude products may be used, an inexpensive source of supply is readily available in the material recovered in the sulfate process for the manufacture of wood pulp.

While the magnesium salt is useful as is the The amount of lignin sulfonate used'will obperature of the process water and many others.

In general, only enough should be used to produce the desired surface-modifying action. For most operations this will be found to lie between about 0.01 to 0.30 lb./ton of feed.

At times or with some conditions as much as 0.50 lb./ton of ore may be required. In general, however, excessive amounts should be avoided. One of the features of the use of the lignin sulfonates as surface modifiers for this purpose is in its successful inhibition of the undesired minerals during th promotion and collection of the desired fraction. Moderate excesses of surfacemodifying agent over the amount necessary to produce the desired selective depression have no particular effect on the process. However, larger excesses may be found to interfere with the promotion of the desired mineral and thus interfere with the desirable result obtained by the presence of smaller amounts. The upper limit, then may be expressed generally as being somewhat less than that amount which depresses the values which it is desired to recover. It is quite surprising that this effective range of small amounts exists whereas the presence of excessive amounts may be harmful.

Because the action of the beneflciating reagents of the present invention is one of surface modification, they may be employed in any one of several ways. If equipment is available for the purpose, a conditioning operation with the surface modifier before carrying out the flotation is usually advantageous. It may even be further advantageous in many cases to condition the flotation feed with the modifying agent before the promoter is added thereto. This is not diiiicult since the lignin sulfonate may be added during the grinding operation or in a pro-conditioning step using a simple mechanical agitator. The surface modifier may be added to the pulp alon with the promoter. It may be used to direct addition to the flotation cell'just prior to or even during flotation. In these various operations it may be used in dry form, as a paste, as aqueous dispersions or suspensions, or in aqueous solution. The latter is preferable in most cases because it simplifies control of the amounts fed, particularly of the small amounts used.

It is a feature of the present invention that it may be employed in any of several ways. It may be used to enable the production of concentrates of equal grade to those obtained by the practice of the prior art while obtaining these concentrates with higher recovery. On the other hand, if a premium on extremely high grade is available, it may be desirable to use the surface modifier to obtain recoveries approximatin those obtainable by the practice of the prior art while increasing the grade to as high a degree a possible. Whichever of these two practices is to be followed will be a factor in determining the quantitles of reagents used. This is true both with respect to the amount of promoter and with respect to the surface-modifying agent of the present invention.

The present invention will be described in detail in conjunction with the following examples which are meant to be illustrative only and not by way of limitation. All parts are by weight unless otherwise noted.

EXAMPLE 1 A copper ore from the southwestern part of the United States assaying approximately 1.20% Cu and containing pyrite. chalcocite, covellite, chalcopyrite, malachite, sphalerite, limonite, quartz, sericite, chlorite, biotite and carbonate was ground to about minus 65 mesh, conditioned at 22% solids with 0.064 lb./ton cresyllc acid, 0.028 lb./ton of a 1:1 mixture of sodium diethyl and disecondary butyl dithiophosphates, and varying amounts of lignin sulfonates, and then'fioated in a Fagergren flotation machine. The results of these tests are summarized in the following table:

Table I Concentrate, cr-

cent Total u Lbs/ton Lignins Reagent Type Tot 81 Cd,

Assay Recov. AS5113 No Lignin Sulfonate used. 15.81 64. 03 0. 44 0. 05 Purified Calcium Lignin Sulfonote 10.00 84. 88 0. 19 0.20 do 14.82 70.64 0. 38 0.05 Crude Sodium Lignin Suli'onate 14.14 72. 4O 0. 355 0.20 .do I. 14.29 08.02 0. 40 l). 05 Neutral Calcium Lignin Sulfonatc 13. 92 73. 10 0. 34:) 0.20 do 11.62 77.83 0.28 O. 04 Basic Calcium Lignin Sulionate ll. 05 81. 47 0. 235 0. 05 Acid Magnesium Lignin Suifonate 15. 60 65. 83 O. 42 0.20 do 17.12 60.80 0.49 0. 05 Neutral Sodium Lignin Sulionate 14. 07 66. 83 0. 42 0.20 .d0 14. 97 68. 33 0. 40 0.05 Neutral Ammonium Lignin Sulionate 12. 88 75. 88 0. 31 0.20 .do 11.00 85.13 0.19

Exllmm2 The primary slime portions of a copper ore from the southwestern United States, obtained by desliming the ore prior to leaching, were treated with 0.32 lb./ton crude calcium lignin sulionate, 0.035 lb./ton potassium ethyl xanthate. 0.06 lb./ton pine oil, and 3.9 lb./ton lime and floated for 8 minutes. From a feed to flotation, assaying 1.04% Cu, of which about half was sulfide copper and about half non-sulfide copper, 85.4% of the-copper was'obtained as a concentrate assaying 17.8% Cu. The tailings assayed 0.16% Cu. a

A similar treatment withoutthe lignin sulfonate gave a recovery or 78.0% of the copper in a concentrate assaying 17.9% On. The tailing from this treatment assayed'0.24% Cu.

EXAMPLE 3 Table II Concentrate, per Telling. cent Zn per cent Lbs./Ton ol Modifier Zn,

' Assay Assay Rccov.

EXAMPLE 4 Table III Concentrate, per Telling. cent Pb per cent him/Ton ol Modifier Assay Assay Rccov.

Exmns 5 A Tri-State ore containing lead and. zinc (about 2.1% Pb and 15.7% Zn) was also treated. The ore was ground and conditioned at 22% solids with 0.055 lb./ton secondary butyl Xanthate, 0.35 lb./ton sodium silicate, 0.10 lb./ton cresylic acid, 0.03 lb./ton sodium cyanide, and 0.02 lb./ton higher alcohol frother known to the trade as 8-23. The conditioned pulp was floated for 2.5 minutes to remove a lead concentrate. The pulp was conditioned with 1.5 lb./ton copper sulfate. 0.60 lb./ton soda ash, 0.18 lb./ton pine oil, and 0.22 lb./ton of American Cyanamid Company 80- dium Aerofloat and then floated for 3 minutes to remove a zinc concentrate. Various lignin sulionates were added to the conditioning steps as follows:

Lignin Sullonate Used Test Lb ll Pb Lb T Z on on n Float 110st None None Mono Calcium 0. 10 0. i0

Crude Calcium. 0.10

The following metallurgical results were ob- A Tri-State lead ore, containing about 2.5 tamed:-

' Table IV Lead Concentrate Zinc Concentrate Telling Assay Test Per Cent Pb Per Cent Zn Per Cent Zn Per Cent Pb Assay Dist. Assay Dist. Assay Dist. Assay Dist. g g

Pb, was ground with 0.035 lb./ton sodium iso- 55 EXAMPLE 6 The lignin sulfonates may be used without cyanide in the separation of sulfides by flotation. The lead-zinc ore used in Example 5 was treated as described in that example except that the use of cyanide was omitted. The following tests were conducted using calcium lignin sulfonate in the first conditioning step only. In the first test no lignin sulfonate was used; in the second test 0.2 1b./ton of calcium lignln sulfonate was used. The metallurgical results are as follows:

Table V Icad'Concentrate Zinc Concentrate I Tailing, Assay Percent Pb Percent Zn I Percent Zn Per cent Pb Assay Dist. Assay Dist. Assay I Dist. Assay Dist. Per Pb Per cent Zn None 7 Exams: 7

An African gold ore, assaying about 0874-0898 oz. Au/ton and containing chalcopyrite, bornite. pyrrhotite, quartz and sericite, was ground to minus 65 mesh and treated as iollows:

1. Conditioned minutes at 22% solids with 0.5 ib./ton crude calcium lignin sulfonate.

2. Conditioned 2 minutes longer with 0.3.lb./ton secondary butyl xanthate, 0.03 lb./t0n of a 1:1 mixture of sodium ethyl and sec. butyl dithiophosphates, and 0.03 lb./ton pine oil.

3. Floated minutes in a Fagergren flotation machine; after 5 minutes of flotation 0.05 lb./ton sec. butyl xanthate and 0.03 1b./ton pine oil were added and flotation continued 5 minutes longer.

A second test was conducted, which was similar in all details to the above-described test except that no lignin sulfonate was used.

. The metallurgical results of both tests are given in the following table. It will be noted that marked improvements in the grade of the concentrate and ratio of concentration resulted in the test employing the lignin sulfon'ate. Losses of gold in the tailings were practically identical in both tests.

Table VI 2. In the beneflciation by froth flotation of a metallic sulfide mineral by means of a promoter selected from the group consisting of the xan thate. dithiophosphoric acids and dithiophosphate types, the improvement which comprises carrying out the separation in the presence of 0.01-0.50 lbs. per ton of a surface-modifying agent for the metal sulfide mineral which agent comprises a salt of a lignin sulfonate.

1o 3. In the beneficiation by froth flotation of a the improvement which comprises carrying out the separation in the presence of 0.01-0.50 lbs. per ton of a surface-modifying agent for at least one of the metal sulfide minerals, which agent comprises a salt of a lignin sulfonate.

ROBERT B. BOOTH. ROY A. PICKENS.

Concentrate LbJ'lon Lig- Feed Assay, nin Bulionate Oz.Au/Ton Ratio of Concentration Per cent Assay GLAD/T011 gg Tailing mail /Ton 1 None 0. 390 13.0; 4. 810 93. 43

We claim: 1. In the beneficiation by froth flotation of a REE ENCES CITED The following references are of record in the metallic sulfide mineral by means of a promoter me of this patent:

selected from the group consisting of the santhate, dithiophosphoric acids and dithiophosphate types, the improvement which comprises carrying out the separation in the presence of 0.01-0.50 lbs. per ton of a surface-modifying 45 3,238,439

agent which comprises a salt of a lignin sulfonate.

UNITED STATES PATENTS Number Name Date 2,130,574 Breerwood Sept. 20, 1938 Bishop Apr. 15, 1941 2,355,365 Cole Aug. 8, 1944 2,407,651 Clemmer Sept. 1'7, 1946 

